The present invention relates to an image pick-up apparatus, an image pick-up program and an image processing program which produce a single combined image from a plurality of picked up images.
Movements of an image pick-up apparatus undesirable in image pick-up operation include not only ones in a direction perpendicular to an optical axis but also ones in a direction along the optical direction (hereinafter referred to as a focus direction). For the movements in the direction perpendicular to the optical axis, a number of techniques have been proposed which prevent fluctuations of an image by shifting part of an image pick-up lens unit in the direction perpendicular to the optical axis.
The movements produced in the focus direction during image pick-up operation result in a blurred image. Particularly when an image is picked up at a high magnification with a macro lens, the movements in the focus direction cause significant blurring in the image.
To address the problem, Japanese Patent Laid-Open No. H10(1998)-312006 has proposed a technique in which auto-focus (AF) operation is first performed, and then, again performed during image pick-up operation, thereby preventing a blurred image due to movements in the focus direction during the image pick-up operation.
Although the technique proposed in Japanese Patent Laid-Open No. H10 (1998)-312006 can prevent a blurred image due to movements in the focus direction during the image pick-up operation, the AF operation during the image pick-up operation moves a focus lens to change an image pick-up magnification (an image magnification).
When a conventional image stabilizer is used to correct image fluctuations in the direction perpendicular to the optical axis, the shutter speed is lower than the value (1/f, where f represents a focal length) at which no image fluctuations generally occur from camera shake, so that the image magnification is greatly changed due to movements in the focus direction.
A change in the image magnification during image pick-up operation produces a displacement of the image, and particularly, significant displacements are seen in the peripheral portion of an image. If the image displacements remain within an allowable range for resolution, visually recognizable blurring is not produced. However, for example when images are picked up at a high magnification or at a low shutter speed with the image stabilizer, the image pick-up operation is susceptible to movements in the focus direction. In other words, the image magnification is greatly changed, which makes it difficult to realize appropriate resolution and deteriorates the image.
Next, data provided by actual measurements is used to calculate movements in the focus direction during image pick-up operation to show how much image deterioration occurs from the movements.
The actual measurement results show that the movement in the focus direction produced in an image pick-up time of 100 msec was 0.35 mm at most. Under image pick-up conditions such as life-size shots in which the image magnification is easily changed, the change rate of image magnification is ±0.44% from the calculation in the following expression (1):
                    M        =                  f                      R            ±                          Δ              ⁢                                                          ⁢              R                                                          (        1        )            where M represents the image magnification, f the focal length (80 mm), and R the object distance.
For example, when an image pick-up device such as a CCD sensor has a short side of 15.12 mm long and a long side of 22.68 mm long, the change rate of the image magnification shown above can be used to calculate an image displacement of approximately ±60 μm in the peripheral portion of the image as shown in FIG. 20. Since an allowable image displacement provided in a resolution chart is approximately ±15 μm in the image pick-up device, the image displacement of 60 μm cannot be analyzed and leads to visually recognizable blurring in the image.
FIG. 21 shows the relationship between the displacement in the peripheral portion of an image and the shutter speed for each image pick-up magnification. It can be seen from FIG. 21 that a higher image pick-up magnification causes a larger change in the image magnification and easily produces degradation of the image.